1. Field of the Invention
The present invention relates to an outboard motor including a transmission device arranged to change a speed of rotation of an engine and to transmit the rotation to a propeller.
2. Description of the Related Art
Because an outboard motor that is installed in a small watercraft is subject to large water resistance, there are times when a planetary gear type transmission device that can make a smooth speed change operation during acceleration or deceleration is applied. For example, JP-B-2785200 suggests a planetary gear type transmission device capable of making shifts to a low speed position during low speed traveling or trolling and to a high speed position during normal traveling.
In the planetary gear type transmission device, a sun gear is fixed so as to be unable to rotate when a shift lever is shifted to the high speed position. A planetary gear revolves on the sun gear in response to rotation of an internal gear when rotation of an engine is transmitted from an input shaft to the internal gear. The revolution of the planetary gear is transmitted from a drive shaft to a propeller via a carrier.
However, in many cases the outboard motor is normally operated in forward and high speed positions. Therefore, the outboard motor requires enhanced durability of each gear of the transmission device for the forward and high speed positions that are normally used. However, in the conventional outboard motor, the planetary gear revolves on the sun gear in the normally used high speed position. Therefore, the outboard motor is normally in a state that a load due to engagement between both the gears is large. This results in a problem that it is difficult to obtain sufficient durability in both of the gears.